The present disclosure represents improvements upon the disclosure of U.S. Pat. No. 6,599,464, incorporated by reference herein in its entirety.
For the metallurgical treatment of molten steel in a converter, oxygen is blown onto the top of the molten steel under the control of a blowing lance. The oxygen lance is subjected to a high thermal load during this top blowing, particularly on its front end. It is therefore typical to cool the lance down intensively. The most effective way to cool an oxygen blowing lance is to thoroughly flush die head of the lance with a large volume of cool water under high pressure. The head of the lance is made of a material with good thermal conductivity, such as copper. High temperature peaks up to 3000 degrees C., particularly at the front end of the lance head which is the focus of heat radiating from the surface of the bath as well as wear and tear lead over time to a reduction in the thickness of the cooling chamber walls found in the head of the lance. If there is not enough distance between the head of the lance and the molten metal, the walls can weaken rapidly and suddenly rupture because they have been weakened. Any release of water vaporizes explosively and damages more than just the metallurgical process. If the lance head ruptures, the treatment of the metal must also be terminated immediately.
To avoid the danger of a water release while simultaneously cooling the lance even when the lance is plunged into the molten steel melt, there is a process (DE 35 43 836 C2), which employs two blowing lances used in rotation. These two lances are cooled alternately and intensively with cool air and then with cool water. The lance in the blow position which is being plunged into the molten steel is cooled with cool air while the other lance outside of the molten steel is cooled intensively with cool water. By repeatedly switching as needed between cool air cooling and cool water cooling the overheating of either lance can be avoided, the advantage of effectively avoiding a water release is the cost of purchasing a second lance.
Additionally, it is true that it is already known how to determine temperature for water cooled blowing lances (JP 62-278217 A) in the treatment of metal, but such a blowing lance is used in another process and with other objectives. In this process the blowing lance is actually submerged in the metal bath and the level of the slag of the molten metal relative to the blowing lance is determined by temperature probes which are staggered inside the lance body. Moreover, in this known process, protection from overheating by detecting the temperature of the lance and controlling the treatment process are not dealt with.